key: cord-0262320-083kbegd
authors: Sonabend, R.; Whittles, L. K.; Imai, N.; Perez-Guzman, P. N.; Knock, E. S.; Rawson, T.; Gaythorpe, K. A.; Djaafara, B. A.; Hinsley, W.; FitzJohn, R. G.; Lees, J. A.; Thekke Kanapram, D.; Volz, E. M.; Ghani, A. C.; Ferguson, N. M.; Baguelin, M.; Cori, A.
title: Non-pharmaceutical interventions, vaccination and the Delta variant: epidemiological insights from modelling England's COVID-19 roadmap out of lockdown
date: 2021-08-18
journal: nan
DOI: 10.1101/2021.08.17.21262164
sha: 295e5372cddf6c8a1f3bc66fa159852521f8a9e6
doc_id: 262320
cord_uid: 083kbegd

Background: England's COVID-19 'roadmap out of lockdown' set out the timeline and conditions for the stepwise lifting of non-pharmaceutical interventions (NPIs) as vaccination roll-out continued. Here we assess the roadmap, the impact of the Delta variant, and potential future epidemic trajectories. Methods: We extended a model of SARS-CoV-2 transmission to incorporate vaccination and multi-strain dynamics to explicitly capture the emergence of the Delta variant. We calibrated the model to English surveillance data using a Bayesian evidence synthesis framework, then modelled the potential trajectory of the epidemic for a range of different schedules for relaxing NPIs. Findings: The roadmap was successful in offsetting the increased transmission resulting from lifting NPIs with increasing population immunity through vaccination. However due to the emergence of Delta, with an estimated transmission advantage of 73% (95%CrI: 68-79) over Alpha, fully lifting NPIs on 21 June 2021 as originally planned may have led to 3,400 (95%CrI: 1,300-4,400) peak daily hospital admissions under our central parameter scenario. Delaying until 19 July reduced peak hospitalisations by three-fold to 1,400 (95%CrI: 700-1,500) per day. There was substantial uncertainty in the epidemic trajectory, with particular sensitivity to estimates of vaccine effectiveness and the intrinsic transmissibility of Delta. Interpretation: Our findings show that the risk of a large wave of COVID hospitalisations resulting from lifting NPIs can be substantially mitigated if the timing of NPI relaxation is carefully balanced against vaccination coverage. However, with Delta, it may not be possible to fully lift NPIs without a third wave of hospitalisations and deaths, even if vaccination coverage is high. Variants of concern, their transmissibility, vaccine uptake, and vaccine effectiveness must be carefully monitored as countries relax pandemic control measures. Funding: National Institute for Health Research, UK Medical Research Council, Wellcome Trust, UK Foreign, Commonwealth & Development Office.

Evidence before this study

We searched PubMed up to 23 July 2021 with no language restrictions using the search terms: (COVID-19 or SARS-CoV-2 or 2019-nCoV or "novel coronavirus") AND (vaccine or vaccination) AND ("non pharmaceutical interventions" OR "nonpharmaceutical interventions) AND (model*). We found nine studies that analysed the relaxation of controls with vaccination roll-out. However, none explicitly analysed real-world evidence balancing lifting of interventions, vaccination, and emergence of the Delta variant.

Our data synthesis approach combines real-world evidence from multiple data sources to retrospectively evaluate how relaxation of COVID-19 measures have been balanced with vaccination roll-out. We explicitly capture the emergence of the Delta variant, its transmissibility over Alpha, and quantify its impact on the roadmap.

We show the benefits of maintaining NPIs whilst vaccine coverage continues to increase and capture key uncertainties in the epidemic trajectory after NPIs are lifted.

Our study shows that lifting interventions must be balanced carefully and cautiously with vaccine roll-out. In the presence of a new, highly transmissible variant, vaccination alone may not be enough to control COVID-19. Careful monitoring of . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

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Despite the UK being the first country to start nationwide vaccination campaigns 1 , the emergence of the Alpha variant of concern (VOC) drove the severe second wave over the 2020-2021 winter leading to a third lockdown in England from 5 January 2021 2 . Informed by mathematical modelling, the UK government published a "roadmap out of lockdown" for England, setting out the conditions for and expected timeline of a step-wise lifting of non-pharmaceutical interventions (NPIs) 3 . Between 29 March and 19 July 2021, NPIs were incrementally lifted as vaccination coverage increased. By 19 July, 87·5% of the adult population in England had received at least one dose of vaccine, and 68·2% had received two doses 4 . The impact of each roadmap step was assessed in real-time against the government's "four tests" before further interventions were lifted: i) continued success of the vaccine programme; ii) evidence of the effectiveness of vaccines against hospitalisation; iii) no risk of overwhelming the NHS; and iv) new VOCs do not change the risk assessment 3 .

The emergence of VOCs, notably the lineages Alpha, Beta, Gamma, and Delta first detected in the UK, 5 South Africa, 6 Brazil, 7 and India 8 respectively -has posed recurring challenges for pandemic control efforts globally. The Delta variant was designated a VOC on 6 May 2021 by Public Health England (PHE) and quickly became the dominant variant in the UK 9 . Delta is substantially more transmissible than Alpha 9,10 , a variant already 50-80% more transmissible than previously circulating variants 5,11 . Delta is also estimated to have a 1·85 to 2·6-fold increase in the risk of hospitalisation 12, 13 . It is also associated with partial immune escape 14 and . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

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The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint consequent reductions in vaccine effectiveness (VE) and cross-protection from prior non-Delta infections 13-18 .

Delta's emergence in the UK in mid-April 19 drove a rapid increase in cases and hospitalisations across all areas of England 9 , prompting the final roadmap step (step four) being delayed by a month to 19 July 20 . Daily case numbers in England started increasing from mid-May 2021, and grew exponentially from mid-June to mid-July, reaching a peak of 56,282 on 15 July. Numbers then unexpectedly and synchronously fell to half that value over the following two weeks, before plateauing and beginning to rise slowly again in August 21 .

Here we quantify the impact of each step of the roadmap from i) school re-opening;

ii) outdoor hospitality and non-essential retail; and iii) indoor hospitality. 3 Our model framework was developed and adapted throughout the epidemic to provide quantitative evidence and epidemiological insights to the UK government. As an update to this work, we show what the impact of the full roadmap would have been in the absence of Delta, and summarise the real-time modelling of policy options that informed the delaying of the final step four. [22] [23] [24] Finally, we assess the potential epidemic magnitude, timing, and main sources of uncertainty after step four under different VE and immune escape assumptions of Delta and the level of transmissibility after NPIs are lifted 25, 26 , taking into account recent trends in case incidence and hospitalisations.

We extended a previously described stochastic SARS-CoV-2 transmission model to include vaccination and to capture multiple variants 27 . We used Bayesian methods to . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint We then used the fitted two-strain model to project the epidemic trajectory after 19

July under different scenarios. For these forward projections, we accounted for seasonality in SARS-CoV-2 transmission and the impact of school holidays on transmission (for full model description and data sources see appendix 1) 28 .

In our model fitting and forward projections, we explored plausible ranges of key epidemiological characteristics of Delta. First, we used estimates of the transmission advantage of Delta over Alpha which were informed by fitting the two-strain model to VAM data. Second, we allowed for imperfect cross-immunity between Alpha and Delta: infection with a pre-Delta variant (e.g. Alpha) provides only 75-100% is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint Fourth, we assumed that vaccines induced long-lasting immunity, but examined varying assumptions about the duration of infection-induced immunity: lifelong or average of six-or three-year duration (appendix 1, section 4.4) 31-33 . Finally, we accounted for the increased severity of Delta relative to Alpha by assuming a 1·85fold increased risk of hospitalisation 13 .

We explored counterfactual scenarios of the impact of the roadmap on the epidemic trajectory in the presence and absence of Delta. We compared the projected number of infections, hospital admissions, and deaths for scenarios with and without Delta, varying cross-protection, VE, and waning immunity as described above. To capture the easing of restrictions at step four, we sampled from a range of values for the reproduction number R, the average number of secondary infections generated by one case, in the absence of natural-and vaccine-induced immunity (R excl_immunity ) that could occur at that stage. Our central scenario assumes contacts increase gradually over an 11-week period after step 4 to a maximum of 40% (low), 70% (central), or 100% (high) above contact rates estimated for the period step three was in place 34 .

Finally, we assessed the impact of delaying step four, planned initially for "not before" 21 June, until 19 July.

To understand the main drivers of uncertainty of the magnitude of the third wave, in the forward projections we systematically varied i) VE against Delta; ii) crossprotection against Delta from prior infection with non-Delta variants; iii) the duration of natural immunity; and iv) the level of transmissibility after step four (appendix 1, is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint section 5.4). We also assessed a further counterfactual scenario where contacts increased to maximum levels immediately after the step 4 date, rather than gradually as in the central scenario.

The funders had no role in study design, data collection, analysis, or interpretation, or writing of the report.

Ethics permission was sought for the study via Imperial College London's standard ethical review processes and was approved by the College's Research Governance and Integrity Team (ICREC reference: 21IC6945).

The model reproduces national (Figure 1) and regional (appendix 1, section 7.1) trends in the SARS-CoV-2 epidemic in England well, including the emergence and eventual dominance of the Delta variant ( Figure 1C ,F) and the July dip in case numbers, hospitalisations ( Figure 1A ,B) and hospital deaths ( Figure 1D ,E). Figure 2 shows estimates of how the reproduction number and population immunity changed over time since December 2020. Overall, while R excl_immunity increased markedly from March to July, as a result of the relaxation of lockdown and then the importation of the Delta variant, the rapid rollout of vaccines progressively increases the gap between R excl_immunity and the effective reproduction number (R t eff , which accounts for the impact of natural-and vaccine-induced immunity on transmission). The Christmas school holidays and accompanying near-lockdown social distancing followed by the third national lockdown in January successfully brought R t eff below the critical threshold of one. This period coincided with a rapid expansion of the . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

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The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint national vaccination programme. By 8 March (step one of the roadmap) when educational institutions re-opened, 43% and 2% of eligible adults (>18 years) had received their first and second vaccine dose respectively 4 . Cases, hospitalisations, and deaths continued to decline and remained at low levels even after schools reopened ( Figure 1) . Although we estimated a slight increase in R t eff after step one, Easter holidays and the roll-out of vaccination maintained R t eff below one ( Figure 1A) when non-essential retail opened (61% and 15% first and second dose coverage respectively by 12 April, step two) 4 . The Delta variant, detected in early April predominantly in London and the North West regions ( Figure 1F ), was designated as a "variant under investigation" on 15 April after increasing numbers of locallyacquired infections with that variant were detected ( Figure 1C ) 19 .

We estimated that R t eff for Alpha remained below one (appendix 1 Figure S17 ) after step two due to increasing population immunity from vaccination, with uptake increasing to 69% and 39% first and second doses respectively by 17 May (step three, resumption of indoor hospitality and inter-household mixing) 4 . However, after initial seeding between late-March and early April ( Figure 1F ) the proportion of Delta variant cases was increasing rapidly across all regions in this period ( Figure 1C and appendix 1 Figure S17 ). This rapidly drove R t eff above one by mid-May -reflecting the 73% (95%CrI: 68%-79%) transmission advantage of Delta compared with Alpha we estimate (Figure 2A ).

The increase in contacts after step three continued to be offset by the increasing vaccine-induced population immunity (Figure 2 , 82% and 60% first and second doses respectively by 21 June) 4 . However, the net impact of this differed qualitatively by variant: we estimated that R t eff for Alpha remained below one through to mid-July, while R t eff for Delta remained above one (appendix 1 Figure S17 ). is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint A further sharp increase in R t eff was then seen in the first half of July; at the time, we and other modelling groups advising the UK government concluded this was a belated result of step 3, but the rapid drop following 11 July (and other data indicating a sex imbalance in case incidence) 35 , suggest that the increase in transmission rates seen in that period resulted from a transient increase in population contact rates, particularly in young men, likely associated with the Euros football tournament. At the time of writing, that decline has reversed, with a gradual increase in case incidence being seen in the first two weeks of August. 21 Figure 2 shows that despite high vaccine coverage in adults, sufficient population susceptibility remains for a third wave to occur as contact rates rise. The proportion protected against infection after vaccination against Delta is substantially lower than for Alpha, and most individuals <18 years have neither been vaccinated or infected.

In this context, Delta's high transmissibility means that population immunity is insufficient to keep R t eff below one. is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint We found that delaying step four until 19 July was beneficial for all scenarios considered, with a much smaller projected wave, although still highly uncertain and sensitive to assumptions around VE against Delta and mixing after NPIs are lifted ( Figure 3 ). The delay allowed the distribution of an additional 2.8 million and 3.8 million first and second doses respectively between 21 June and 19 July 4 , reducing the projected future peak of daily hospital admissions by three-fold from 3,400 (95%CrI: 1,300-4,400) to 1,400 (95%CrI: 700-1,500) in the central scenario of gradually increasing contact rates. It also reduced the total predicted deaths between 21 June 2021 and 1 June 2022 by approximately 15% (appendix 1 Table S16 ). Had contact rates increased more abruptly after step 4, the reductions in peak hospital admissions and deaths caused by delaying until 19 July would have been substantially greater (see appendix 1, section 7.2). However, trends in cases, hospital admission and death data in the months up to mid-August 2021 suggest that contacts have increased gradually since step 4, in line with the assumptions of our central scenario ( Figure 1B,E) .

In sensitivity analyses, we found that VE was the main driver of uncertainty of the magnitude of the third wave, followed by the level of mixing after NPIs are lifted, the level of cross-immunity, and waning immunity. The rate at which prior immunity waned had a greater impact on expected total infections but only minimally impacted expected hospitalisations or deaths ( Figure 3 and appendix 1, section 7. 3).

We project future deaths predominantly in fully vaccinated individuals 75+ years of age, given the high vaccine uptake in the most vulnerable age groups. We also anticipate a substantial number of deaths amongst fully vaccinated adults aged 50 -74 years (appendix 1, Figure S25 ). is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint (appendix 1, section 3.1 and 4.4) .

Mathematical models are valuable tools to inform the design, monitoring, and evaluation of vaccination programmes 36 . In this study, we retrospectively assessed England's "roadmap out of lockdown". By extending our evidence synthesis framework to account for vaccinations and multiple variants, we reliably captured the past epidemic and quantified the impact of each phase of lifting interventions and the emergence of the Delta variant on transmission 27 .

We show that the roadmap was successful in mitigating the increase in mixing due to lifting NPIs, by increasing population-level immunity through the mass vaccination programme. Our projections show that in the absence of the Delta variant, lifting NPIs at the planned earliest date of the final step (21 June) would not have resulted in a substantial third wave (appendix 1 Figure S24 ). This emphasises the importance of carefully aligning the lifting of interventions with immunity levels in the population.

Israel rapidly vaccinated a high proportion of their population throughout their reopening plan, and then implemented vaccination "passes" for entry to high-risk settings 37, 38 . Conversely, case incidence and hospitalisations are currently surging in several US states, due to restrictions being released when vaccination coverage was too low to give sufficient population immunity 39 .

Our analyses emphasise the significant impact that the emergence of Delta had on the planned roadmap (Figure 2 and Figure 3 ). Similar to previous studies, we estimated that Delta has an average 73% (95%CrI: 68%-79%) transmissibility advantage over Alpha 10 . Together with reductions in VE for Delta, this drove a rapid increase in cases and hospitalisations from mid-May that was not offset by the vaccination programme 16, 17 . A similar displacement of Alpha and a surge in cases is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint was observed in India where Delta was first detected 40 . The dominance of Delta has now led to a tightening of restrictions in many countries, including in Israel, the country with the fastest vaccination rollout 41 .

Across all the scenarios we examined, delaying step four until 19 July was beneficial ( Figure 3 ) as it allowed more individuals to be vaccinated. In the central scenario, this delayed and reduced the peak of hospitalisations by three-fold and reduced total deaths between June 2021-2022 by approximately 15%.

We project a substantial autumn wave of transmission, but with large uncertainty around the resulting peak hospitalisations and total deaths. This uncertainty is driven by imperfect knowledge of VE against Delta (appendix 1, Figure S3 ) and thus the overall level of population immunity (accounting for waning and imperfect crossprotection -see appendix 1, section 7.3). At high vaccine coverage, even a difference of 98% vs 95% in VE against mortality translates to a doubling of projected deaths. 42 Furthermore, the transmission intensity (R t eff ) in the coming months will depend on and how high and how quickly population contact rates will increase, the continued use of face coverings 43 , social distancing, and adherence to case isolation 44, 45 . The rapid exponential growth in case incidence in the first half of July illustrates the high transmission levels that could be reached if contact rates approach pre-pandemic levels in the coming months. Fortunately, that increase in contact rates, likely caused by the Euro 2020 football tournament 35 , proved transient, and was then followed by the synchronous self-isolation of contacts alerted through NHS test and trace 46 and the start of school holidays a week later -driving transmission down for the last two weeks of July. Polls showed that 57% of UK adults were worried about the removal . CC-BY-NC-ND 4.0 International license It is made available under a perpetuity.

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The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint of legal restrictions and 66% would continue to wear a face covering after 19 July 47 .

The average number of contacts is still much lower than pre-pandemic levels 48 , and our central scenario which assumes a gradual increase in contact rates most closely reflects current trends (Figure 1 ). We estimate that this slow increase in contact rates after 19 July will dampen the peak of hospitalisations and total deaths ( Figure 3 and appendix 1 Figure S24 ) compared to an abrupt increase.

We have focused on deaths and hospital admissions as primary outcomes in our analysis, given the impact of hospitalisation on NHS capacity. However, an estimated 1.5% of individuals in the UK were experiencing symptoms of long-COVID (symptoms lasting more than 4 weeks) on 4 July 2021 49 . Although our estimates of infections and cases over time may capture this wider burden of disease, 50 we did not explicitly quantify this. Overall infection levels also determine the risks of new VOCs emerging within the UK with the risk increasing with transmission levels.

Independently of VOCs emerging, the duration of infection-and vaccine-induced immunity for all SARS-CoV-2 lineages remains a key unknown and will determine long-term transmission dynamics. Better characterising the duration of immunity against both infection and severe disease will be important for informing vaccination booster programmes.

Our analysis has a number of limitations. We did not consider re-introduction of NPIs, vaccination of <18 year-olds, nor booster doses in our projections. These measures, if introduced, may partially mitigate the third wave. Vaccination of [16] [17] year olds is planned to start in late August, and clinically vulnerable 12-15 year-olds are also eligible for vaccination 51, 52 . However, given the age-profile of projected hospitalisations and deaths (appendix 1, Figure S25 ) we anticipate expansion of is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint eligibility may only have a moderate impact. Although we modelled heterogeneity by age in mixing patterns and in vaccine uptake, we did not explicitly model other factors (e.g. by occupation, sociodemographic, and ethnic groups 53, 54 ) which may affect both the risk of infection and vaccine uptake. Vaccine uptake was also assumed to be independent of mixing patterns or viral transmission. Groups of individuals who are both at high risk of infection and less likely to take the vaccine may lead to continued outbreaks amongst vulnerable populations and reduce the overall impact of vaccination. Although we explored the impact of waning of natural immunity, here we assumed vaccine-induced immunity did not wane over the timescales we considered in this paper. Our analysis focused only on outcomes directly related to COVID-19: we did not consider the impact on health services, other diseases, mental health, or the economic impact of measures.

In summary, our study shows how the phased lifting of NPIs in England, coordinated with vaccine roll-out, has been largely successful at keeping hospitalisation and is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted August 18, 2021. 

AC has received payment from Pfizer for teaching of mathematical modelling of infectious diseases. KAMG has received honoraria from Wellcome Genome Campus for lectures and salary support from BMGF and Gavi through Imperial College London for work outside this study. All other authors declare no competing interests.

All data files and source code are available here: https://github.com/mrcide/sarscov2-roadmap-england is the author/funder, who has granted medRxiv a license to display the preprint in (which was not certified by peer review) preprint

The copyright holder for this this version posted August 18, 2021. ; https://doi.org/10.1101/2021.08.17.21262164 doi: medRxiv preprint

Covid-19 vaccine: First person receives Pfizer jab in UK -BBC News

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SARS-CoV-2 variants of concern and variants under investigation in England Technical Briefing 15

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COVID-19) in the UK

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Public Health Scotland COVID-19 Statistical Report As at 28

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DELVE: Report on face masks for the general public

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49 Office for National Statistics. Prevalence of ongoing symptoms following coronavirus (COVID-19) infection in the UK

Persistent symptoms following SARS-CoV-2 infection in a random community sample of 508,707 people

Department for Health & Social Care. JCVI statement on COVID-19 vaccination of children and young people aged 12 to 17 years: 15

JCVI issues updated advice on COVID-19 vaccination of young people aged 16 to 17

Coronavirus (COVID-19) Infection Survey: characteristics of people testing positive for COVID-19 in England and antibody data for the UK -Office for National Statistics

54 Office for National Statistics. Coronavirus and vaccine hesitancy, Great Britain -Office for National Statistics

We thank all the colleagues at Public Health England (PHE) and frontline health professionals who not only have driven and continue to drive the daily response to the epidemic but also provided the necessary data to inform this study. This work would not have been possible without the dedication and expertise of said colleagues and professionals. The use of pillar-2 PCR testing data, vaccination data,